[moderation] [serial?] KCSAN: data-race in pty_stop / pty_unix98_ioctl (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1f4a222b0e33 Remove long-stale ext3 defconfig option
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=165f7b34580000
kernel config: https://syzkaller.appspot.com/x/.config?x=bafeb347352dd60e
dashboard link: https://syzkaller.appspot.com/bug?extid=b6077fe3d037cf2a3a56
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [gre...@linuxfoundation.org jiri...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/785e68511950/disk-1f4a222b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2366f9786f09/vmlinux-1f4a222b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1ec7c0f5bb09/bzImage-1f4a222b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b6077f...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in pty_stop / pty_unix98_ioctl

write to 0xffff8881199ed5d5 of 1 bytes by task 23416 on cpu 0:
pty_set_pktmode drivers/tty/pty.c:-1 [inline]
pty_unix98_ioctl+0x2c0/0x2e0 drivers/tty/pty.c:651
tty_ioctl+0x7d8/0xb80 drivers/tty/tty_io.c:2792
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x1816/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881199ed5d5 of 1 bytes by task 12325 on cpu 1:
pty_stop+0x3f/0xe0 drivers/tty/pty.c:339
__stop_tty drivers/tty/tty_io.c:746 [inline]
stop_tty+0x8d/0xe0 drivers/tty/tty_io.c:766
n_tty_receive_char_flow_ctrl+0xec/0x1a0 drivers/tty/n_tty.c:1238
n_tty_receive_char_special drivers/tty/n_tty.c:1343 [inline]
n_tty_receive_buf_standard+0x4d2/0x2f10 drivers/tty/n_tty.c:1588
__receive_buf drivers/tty/n_tty.c:1624 [inline]
n_tty_receive_buf_common+0x805/0xbe0 drivers/tty/n_tty.c:1723
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1769
tty_ldisc_receive_buf+0x66/0xf0 drivers/tty/tty_buffer.c:387
tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:445 [inline]
flush_to_ldisc+0x148/0x340 drivers/tty/tty_buffer.c:495
process_one_work kernel/workqueue.c:3263 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3346
worker_thread+0x582/0x770 kernel/workqueue.c:3427
kthread+0x489/0x510 kernel/kthread.c:463
ret_from_fork+0x122/0x1b0 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 12325 Comm: kworker/u8:13 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Workqueue: events_unbound flush_to_ldisc
==================================================================


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